Two radicals can be added if and only if they have the same number/variable(s) under the square root- or radicand. Often, you will need to simplify radicals first in order to tell if they can be combined. Here, we simplify radicals and multiply by coefficients out front to see if we have "like radicands" that can be combined. The numbers outside the square roots will be added/subtracted, and the number inside the root will remain unchanged.